1. Field of the Invention
The invention relates to a false-closure detection device for electrical consumers which receive load current from a supply voltage via a power output stage having at least two power switches activated by a control device with control signals, a high-side switch and a low-side switch and which form a load circuit; the system includes a measurement and diagnostic device for the detection of faults.
Devices of the generic type serve for the detection of faults in a load circuit of an electrical consumer which is overloaded or has false closures to ground or to a supply voltage.
2. Description of the Related Art
German published, non-prosecuted application DE 40 30 533 A1 discloses a system for monitoring a consumer in connection with an internal combustion engine or a motor vehicle. The consumer, in particular an electric drive which is activated by means of a bridge circuit output stage, is monitored and a delayed alarm signal is generated by comparing potentials in the region of the consumer or the output stage with predetermined threshold values derived from normal operation. The time delay depends on the magnitude of the control signal.
In that configuration there is provided a measuring path which lies directly parallel to the electrical consumer in the load branch, the output signals of which are evaluated by means of comparator stages. The consumer in that case lies in the bridging branch of a bridge formed by power-circuit position switches.
German published, non-prosecuted application DE 44 03 375 A1 discloses a device and a method for controlling an inductive consumer. There, an inductive consumer with switches arranged in an H-bridge is controlled. For monitoring the device, the H-bridge is briefly switched off. As a result, there is induced at the terminals of the consumer a voltage which is opposed to the bridge cross voltage of the switched-on state. The voltage drop across the consumer is compared with a setpoint value and an error signal is triggered if there is any deviation from the setpoint value.
In that prior art device, the measured value is picked off parallel to the electrical consumer in the bridging branch and it is evaluated by means of comparators.
German published, non-prosecuted application DE 38 42 426 A1 discloses a circuit configuration for controlling and monitoring a consumer in a bridge circuit. That circuit configuration controls and monitors an electrical consumer in the diagonal of a bridge circuit comprising four FET power-switching elements. The circuit configuration is used to monitor the overloading of the circuit of the consumer, which is switched off temporarily or until the fault is rectified.
In that prior art circuit configuration, the measuring path lies parallel to the electrical consumer in the bridging branch of the bridge.
European patent application EP 0 055 816 discloses an electronic circuit with power switches in bridge arrangement, an inductive consumer lying in the bridging branch. The voltage across the bridging branch is evaluated for measuring and evaluation purposes in a downstream evaluation circuit.
In the publication "Elektronik", vol. 13, 1993, pages 86-90, there is disclosed a circuit which involves a monolithic H-bridge driver with protective and diagnostic circuits. Represented in FIG. 1 of the publication there is shown a motor as the electrical consumer in the load circuit. The load current of the motor is controlled in two directions. By means of relays and for diagnostic or measuring purposes, the bridging branch, or the voltages of the terminals of the electrical consumer, is or are interrogated and measured. The measuring device senses the "dangerous state" and evaluates it and precautions for the activation of the power switches are taken by means of a control stage. For diagnostics, the evaluated measuring signals are externalized by means of suitable buffer circuits and excess temperature, overcurrent, consumer interruption and undervoltage can be read off at the status output. By suspending the time delay of the temperature hysteresis and by skillful sequencing when interrogating the input signals, it is additionally possible to distinguish between a short circuit of output 1 or 2 to ground and U.sub.bat.
The above-mentioned publications have in common that the measuring voltage for an electrical consumer operated in an H-bridge is picked off directly at the electrical consumer and evaluated by means of suitable circuits, generally comparator circuits. As a result, certain operating faults can be sensed and evaluated and precautions can be taken by means of control circuits to ensure that the fault does not lead to appreciable consequences.
It is a common disadvantage of all those prior art configurations that a defect at the power-circuit position switches themselves cannot be detected and evaluated, or only to a limited extent.